Internal combustion engines operating with more than one fuel are known. Certain engines use two or more fuels having different reactivities. One example of such an engine can be seen in U.S. Patent Application Pub. No. 2011/0192367, which was published on Aug. 11, 2011 to Reitz et al. (hereafter, “Reitz”) herein incorporated by reference in its entirety. Reitz describes a compression ignition engine that uses two or more fuel charges having two or more reactivities in a process that is sometimes referred to as reactivity controlled compression ignition (“RCCI”). According to Reitz, two fuels can be introduced into the combustion chamber at different times to produce stratified regions having different reactivities that will auto-ignite under compression. The relative reactivities of the fuels and timing of their introduction determines in part ignition timing, and duration and temperature of combustion that, in turn, can affect combustion rate, engine power output and emissions. In fact, the two-fuel methodology disclosed in Reitz is described as reducing engine emissions in accordance with government regulations without the assistance of other emission reduction technologies such as exhaust gas recirculation (“EGR”).
EGR is a technology in which a portion of the exhaust gasses expelled from the combustion process are redirected and combined with the engine intake air to reduce emissions such as nitrogen oxides (NOX). The presence of exhaust gasses in the combustion chamber at the start of combustion lowers the relative oxygen ratio and the maximum combustion temperature that otherwise promotes NOX formation. The dual reactivity system of Reitz and EGR therefore offer two different control parameters for reducing emissions. However, because of their different operational methodologies and characteristics, it has thus far not been understood whether or how they could work in conjunction with one another.